A spectator airlifted to hospital after being hit by a rally car is in a "life-threatening" condition, police said.
The man, in his fifties, was taken by helicopter to Aberdeen Royal Infirmary after the incident at the Granite City Rally in Durris Forest, outside the city.
He has injuries to his leg and pelvic injuries which are described as life-threatening, Grampian Police said.
Police said a rally car had left a forest track and collided with four male spectators.
The other three men were taken to hospital by ambulance at around 11.20am on Saturday, Grampian Police said.
One of them received minor injuries, and two had "serious injuries which are described as not life-threatening".
One was a competitor in the Scottish Rally Championship, the Aberdeen and District Motor Club said.
The accident happened after a car had previously come off the track, and spectators had come to assist it getting back on the road, it said.
A second car then came off the track in the same spot, the club said in a statement.
In the statement posted on the club's website, it said: "A series of events contributed to the incident, which happened following a slight crest on a straight section of forest track.
"Car 152, driven by Rachel Medich (Nissan Micra), initially went off the track on the left-hand side of the road. As it was a straight section of track, spectators were lining both sides of the road.
"After the Micra came to a halt, approximately six feet off the track, a number of spectators went to offer assistance and help get car 152 back on to the road.
"A few minutes later, car 154, driven by Simon Frazer Hay (Peugeot 205) went off at the same spot and collided with a number of spectators.
"Immediately the stage was closed and the emergency services and rescue crews were sent into the stage. An ambulance was also dispatched immediately."
The rally was cancelled following the incident, which happened in the opening stages of the event.
Police are investigating what happened.
Inspector Ewan Innes, from Grampian Police, said: "This is a very unfortunate incident and our thoughts are with those who are injured and their families.
"Inquiries are at an early stage and I have been in contact with the procurator fiscal's office to discuss the incident.
"At this time we are deploying collision investigators to the scene and we will be working closely with the procurator fiscal, race organisers and Aberdeenshire Council to carry out a full inquiry into the circumstances of the incident."
The Granite City Rally is described as "the biggest motorsport event in the north-east of Scotland", and involves more than 100 crews starting from the Thainstone Agricultural Centre, near Inverurie.
The course runs for 44 miles (71km) in five stages and is the third round in the Scottish Rally Championship.
Ian Shiells, clerk of the course, said: "Obviously this is a sad incident and our thoughts are with the injured spectators.
"Safety is always paramount in Scottish rallying and we thank the rescue crews and medical staff for their swift response to the incident."